Electrolytic cleaning and corrosi on removal process

ABSTRACT

A PROCESS FOR REMOVAL OF FOREIGN MATERIAL AND CORROSION PRIMARILY FROM METALLIC SURFACES UTILIZING A PARTICULAR CHEMICAL BATH IN CONJUNCTION WITH ELECTROLYSIS.

United States Patent 3,756,931 ELECTROLYTIC CLEANING AND CORROSION- REMOVAL PROCESS Cyrus M. De Boer, Rte. 2, Newaygo, Mich. 49337 No Drawing. Filed Sept. 13, 1971, Ser. No. 180,179 Int. Cl. C23b 3/02, 1/04, 1/06 US. Cl. 204-14l.5 3 Claims ABSTRACT OF THE DISCLOSURE I A process for removal of foreign material and corroslon primarily from metallic surfaces utilizing a particular chemical bath in conjunction with electrolysis.

BACKGROUND OF THE INVENTION The removal of corrosion and foreign materials from work surfaces is a necessary step in preparation for painting or plating operations. A number of solvents such as carbon tetrachloride, detergents, and acid or alkaline solutions are in general use to remove grease, oil, and soluable foreign materials. The reduction and loosening of corrosion is a different type of chemical reaction, and a number of baths have been developed for this purpose. Those in current use tend to be incomplete in their action, or require excessive time to produce a given degree of cleaning. Examples of a chemical approach to this problem have been noted in the following patents, which have been selected as illustrative of attempts to use two of the chemical ingredients of the bath in which the present invention is carried out: Healy, Jr. et al., 2,408,424, 1946; McNally, 2,714,094, 1955; Newman, 2,828,193, 1958.

SUMMARY OF THE INVENTION The process provided by the present invention appears to be a combination of chemical and electrolytic action, and it is not clear whether or not the electrolysis alters the chemical reaction per se. It is abundantly clear, however, that the action of the bath without the electrolysis is far less effective. The preferred bath utilized by this invention is based on a water solution of ferric sulphate and ammonium bifluoride at two pounds of each to a gallon of Water supplemented by four ounces by weight of sodium sulphate and one liquid ounce of a wetting agent. This bath is subject to a direct current of four to six volts, with the pieces being processed placed electrically in the anode position in the bath (the reverse of the electrical position for plating).

DESCRIPTION OF THE PREFERRED PROCEDURES The process provided by the present invention utilizes a bath which has considerable utility as a cleaning agent, without the assistance of electrolysis. This bath is described and claimed in my co-pending application Ser. No. 180,- 186, filed concurrently with the present application. The primary ingredients of this bath are ferric sulphate and ammonium bifluoride, each of these ingredients being present in a particular range of proportions. A series of experiments following the accidental discovery of the interaction between ferric sulphate and ammonium bifluoride has produced interesting results. Work pieces contaminated with rust and mill scale were not cleared to any appreciable extent by either the use of ferric sulphate or ammonium bifluoride acting along in any concentrations. Ammonium bifluoride seemed to produce a slight loosening of the contamination, which required diligent application with a wire brush for removal of the major portion of the corrosion. Since it has been determined that the best form of the bath utilizes two pounds of the ferric sulphate together with two pounds of the ammonium bifluoride, the experimental program was directed primarily Patented Sept. 4, 1973 to determine the range of operability on either side of this preferred proportion. Holding the ferric sulphate at two pounds, the quantity of the ammonium bifluoride was increased from zero in progressive steps. Up until the eight ounce point was reached, the action of the bath was negligible to slight. With the presence of sixteen ounces of ammonium bifluoride, the action became quite good, and the increase to thirty-two ounces produced the preferred proportion. Continued addition of ammonium bifluoride above this proportion produced no increase in the performance of the bath.

A second phase of the experimenting began with two pounds of the ammonium bifluoride in a gallon of water, and the progressive increase in ferric sulphate from zero. Here, again, the action of the bath was negligible to slight until the quantity of the ferric sulphate present had increased to eight ounces. At sixteen ounces, the bath became reasonably effective, with the performance increasing progressively until the two pound quantity had been attained, at which there appeared to be the most effective relationship of the ferric sulphate and the ammonium bifluoride.

The addition of one liquid ounce of a wetting agent, which is a conventional detergent liquid, seemed to assist slightl in the removal of solid particles from the surface being cleaned. It was also noted that when test pieces were rinsed after immersion in the bath, the pieces that had been subject to the bath containing this quantity of the wetting agent showed a slightly clearer color than those that had been treated by the bath without the wetting agent. In summary, the wetting agent seems to be preferable, but not vital. The addition of sodium sulphate, however, clearly produces an interaction with the ferric sulphate and ammonium bifluoride that appears to be in the nature of a catalytic reaction. The addition of one ounce of sodium sulphate to the mixture containing two pounds each of ammonium bifluoride and ferric sulphate produced a much brighter surface on the test pieces, and decreased the time required to obtain any given degree of brightness. The use of two ounces of sodium sulphate produced a significant further improvement, but subsequent increase to three ounces seemed to cancel the effect of the sodium sulphate entirely. At four ounces, the action of the solution seemed to be blocked to a very considerable extent. The degree of blockage was further increased with continued increase in the quantity of sodium sulphate. Test pieces used in the above experiments were patches of perforated steel sheet that had been subject to an acid bath and to ordinary atmospheric corrosion (primarily ordinary rust).

The preparation of the various forms of the bath involves nothing unusual. The ferric sulphate is usually obtained in granular form, and the ammonium bifluoride in the form of flakes. The ferric sulphate is preferably first emulsified in a blender, with the addition of enough water to make a paste. The ammonium bifluoride is then added, and the resulting mix added to a gallon of water. The wetting agent and the sodium sulphate are then added as the final step. It is recommended that this mixture be used below F. to avoid the generation of objectionable fumes. It also appears that a temperature in excess of F. seems to block the action of the bath. It should also be noted that air or mechanical agitation of the bath while the pieces are immersed will increase the rate of action.

When the bath is subject to an electric current in the manner of a reversed plating operation, a rather striking result takes place. With the application of five volts direct current, and with the parts being treated connected in the electrical position of anodes, the time required to achieve a given degree of cleaning was approximately one half of the time required by the bath alone. It has also been discovered that the proportions of sodium sulphate in the bath for best performance are diiferent when electrolysis is used. The optimum amount of sodium sulphate in the bath subject to electrolysis is four ounces (in conjunction with the bath proportions specified previously), and substantial blocking action of the solution did not seem to take place until approximately eight ounces of the sodium sulphate was used. In summary, the action of the electrolysis was better over the entire range of proportions specified for the bath, and continued to improve with further increase in the sodium sulphate up until the four ounce point. While the use of five volts appears to be best, a range of four to six volts is acceptable. Beyond six volts, there appears to be some degree of attack on the base metal of the pieces being processed. At the optimum proportions, the action of the bath is so quick as to be startling. Heavily rusted pieces seemed to be cleaned almost instantly as they are immersed. The electrolytic process is much more effective on the removal of such dense forms of corrosion as mill scale. The electrolytic process seems to be most eifective, however, on ferrous metals, where primary concern is the removal of oxide coatings. In the case of aluminum, copper, brass, and other such nonferrous materials, the removal of oxides alone is best accomplished by the bath acting without the electrolysis.

It is interesting to note that coninued use of the bath in the electrolytic process does not seem to involve a degeneraion or contamination of the solution. It is not necessary to dump the bath out periodically, and replace it. The sludge formation in the bath is not composed of hard particles, and may be appropriately drained off periodically. This practice is normally followed by replacement of the solution for quantity purposes only, as the ingredients appear to require no regeneration. The use of a conventional alkaline cleaning bath after the parts have been subject to the electrolytic process described above tends to preserve the brightness of the parts.

What is claimed is:

1. A method of removing corrosion from workpiece surfaces, said method comprising:

(a) placing workpieces in a bath containing the following ingredients:

(1) at least sixteen ounces by weight of ferric sulphate (2) at least eight ounces by weight of ammonium bifiuoride (3) one gallon of Water (b) subjecting said workpieces to four to six volts of direct electric current as an anode in said bath.

2. A method as specified in claim 1, wherein said bath additionally includes two to four ounces of sodium sulphate.

3. A method as specified in claim 1, wherein said bath additionally includes at least one ounce (liquid measure) of a wetting agent.

References Cited UNITED STATES PATENTS 3,627,654 12/1971 Petit 204 R 2,408,424 10/1946 Healy 204145 R FOREIGN PATENTS 1,082,409 9/1967 Great Britain 204-145 OTHER REFERENCES Anodic Pickling of Iron and Steel, by R. Muller and L. Harant, The Electrochemical Society Preprint 69-28, Apr. 27, 1936, pp. 315-323.

JOHN H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner US. Cl. X.R. 

